docs: iio: add documentation for interfacing tools

Add documentation for IIO interfacing tools describing the available
tools which can be used to retrieve data from IIO sysfs.
Reference this documentation in adis16475.rst

Signed-off-by: Ramona Gradinariu <ramona.gradinariu@analog.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20240528142409.239187-6-ramona.gradinariu@analog.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>